Akira Fukushima, Hironori NAKAJIMA, Tatsumi Kitahara, Performance Evaluation of an Anode-supported Honeycomb Solid Oxide Fuel Cell, ECS Transactions, 10.1149/05048.0071ecst, 50, 48, 71-75, 2013.05, [URL], An anode-supported honeycomb SOFC that can achieve high power density and enhanced durability was developed. Electrolyte layer of 8YSZ (8 mol% yittria stabilized zirconia) is employed by dip-coating an anode honeycomb substrate of Ni/YSZ, followed by being coated with cathode layer of La0.7Sr0.3MnO3. Current-voltage and current-power density characteristics of the cells having different anode and cathode flow channel configurations at 850℃ were measured. The results show promising performances of the cell as a starting point to develop stacks composed of multiple honeycomb cells..

中島 裕典，許斐 敏明，北原 辰巳，伊賀上 聡, 円筒型マイクロ固体酸化物形燃料電池のインピーダンス解析 (第２報 アノード・カソード過電圧分離解析）, 日本機械学会論文集（B編）, 75巻755号，pp.1517-1523, 2009.07, [URL], The present paper addresses a separate overpotential analysis of the anode and cathode of a practical solid oxide fuel cell (SOFC). Electrochemical impedance spectroscopy with two-electrode set-up is used for the analysis of a micro tubular SOFC having anode-supported electrolyte. This cell is composed of an Ni/(ZrO_2)_<0.9>(Y_2O_3)_<0.1> cermet anode, an La_<0.8>Sr_<0.2>Ga_<0.8>Mg_<0.2>O_<2.8> electrolyte, and an La_<0.6>Sr_<0.4>(Co_<0.2>Fe_<0.8>)O_3 cathode. Measurements are carried out for the cell operated at 700℃ with varying flow rate and composition of H_2-N_2 mixture gas fed in the anode. In our previous study, the anode and cathode impedances have been found to appear in low and high frequency regions, respectively. Therein, the Ohmic resistance, and the charge and mass transfer resistances at the anode and cathode were evaluated. In the present study, the Ohmic, activation and concnetration overpotentials are then evaluated by integration of those resistances. The anode and cathode activation overpotentials are found to be separated using the Butler-Volmer equation. Thereby the concentration overpotential of the anode is also found to be separated by subtracting the anode activation overpotential from the anode overpotential, while the cathode concentration overpotential is found to be negligible. The separation of the overpotentials is successfully confirmed by the observation of the variation of the overpotentials in conjunction with the variation of the anode gas flow rate and composition, giving the exchange current densities. The analysis shows that decreases in the anode activation overpotential and concentration overpotential including the Nernst loss imporove the cell performance..

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中島 裕典，許斐 敏明，北原 辰巳，伊賀上 聡, 円筒型マイクロ固体酸化物形燃料電池のインピーダンス解析(第1報 アノード・カソードインピーダンス分離解析）, 日本機械学会論文集（B編）, 75巻755号，pp. 1510-1516, 2009.07, [URL], A separate analysis of the anode and cathode impedances of a practical solid oxide fuel cell (SOFC) has been performed. Electrochemical impedance spectroscopy is used for the analysis of a micro tubular SOFC havig anode-supported electrolyte with two-electrode set-up. This cell is composed of an Ni/(ZrO_2)_<0.9>(Y_2O_3)_<0.1> cermet anode, an La_<0.8>Sr_<0.2>Ga_<0.8>Mg_<0.2>O_<2.8> electrolyte, and an La_<0.6>Sr_<0.4>(Co_<0.2>Fe_<0.8>)O_3 cathode. Measurements are carried out for the cell operated at 700℃ with varying flow rate and composition of H_2-N_2 mixture gas fed into the anode and those of air-O_2 mixture gas fed into the cathode. The anode and cathode impedances are thereby found to appear in low and high frequency regions, respectively. A common equivalent circuit model is applied for the complex nonlinear least squares curve fitting of impedance spectra to acquire the resistances and capacitances of the charge and mass transfers at the anode and cathode, and the cell Ohmic resistance. Then variation of those parameters of the equivalent circuit in accordance with anode gas feed conditions are obtained for the practical SOFC. They are useful parameters for health diagnosis of SOFCs..

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Hironori NAKAJIMA, Toshiaki KONOMI, Tatsumi KITAHARA, and Hideaki TACHIBANA, Electrochemical Impedance Parameters for the Diagnosis of a Polymer Electrolyte Fuel Cell Poisoned by Carbon Monoxide in Reformed Hydrogen Fuel, Transactions of the ASME, Journal of Fuel Cell Science and Technology , 5, 041013, 2008.11, [URL], We have investigated the behavior of an operating polymer electrolyte fuel cell (PEFC) with supplying a mixture of carbon monoxide (CO) and hydrogen (H2) gases into the anode to develop the PEFC diagnosis method for anode CO poisoning by reformed hydrogen fuel. We analyze the characteristics of the CO poisoned anode of the PEFC at 80°C including CO adsorption and electro-oxidation behaviors by current-voltage (I-V) measurement and electrochemical impedance spectroscopy (EIS) to find parameters useful for the diagnosis. I-V curves show the dependence of the output voltage on the CO adsorption and electro-oxidation. EIS analyses are performed with an equivalent circuit model consisting of several resistances and capacitances attributed to the activation, diffusion, and adsorption/desorption processes. As the result, those resistances and capacitances are shown to change with current density and anode overpotential depending on the CO adsorption and electro-oxidation. The characteristic changes of those parameters show that they can be used for the diagnosis of the CO poisoning..

星子 琢也, 中島 裕典, 許斐 敏明, 北原 辰巳, 固体高分子形燃料電池の拡散インピーダンス解析によるカソード電極触媒表面の水膜厚さの推定, 日本機械学会論文集(B編), 第74巻第741号, pp.1176-1182., 2008.06, [URL], We have analysed the diffusion impedance of a polymer electrolyte fuel cell (PEFC) by electrochemical impedance spectroscopy (EIS). As a result, we derive oxygen diffusion distance d adjacent to the cathode electrode (catalyst layer) assuming planar oxygen diffusion in a thin water layer unlike the conventional flooded-agglomerate model and gas phase diffusion model in a gas diffusion layer. The experimental results and their analyses show that δ agrees with a value reported from our previous ex-situ measurement. Moreover, δ gives reasonable concentration overpotentials. Increasing current density and gas humidification brings about the growth of S. It supports that δ corresponds to the thickness of the accumulated product water in liquid state at the cathode electrode. Thus EIS analysis of the diffusion impedance can be used to diagnose the water accumulation at the cathode electrode. This result enables the prediction of the flooding and drying-up of PEFCs and assures their stable operation..

Akira FUKUSHIMA, Shota KOTAKE, Hironori NAKAJIMA, and Tatsumi KITAHARA, Performance of an Anode-supported Honeycomb Solid Oxide Fuel Cell, Fuel Cell and Hydrogen Production Symposium “Alternative Materials and Devices” [International Hydrogen Energy Development Forum 2013] (第62回固体イオニクス研究会）, 2013.01, We have developed an anode-supported honeycomb SOFC that can achieve high power density and enhanced durability. Electrolyte layer of 8YSZ is employed by dip-coating on an anode honeycomb substrate of Ni/8YSZ, followed by being coated with cathode layer of LSM. We measure the current-voltage and current-power density characteristics of the cells having different anode and cathode flow channel configurations at 850℃. The results exhibit promising performances of the cell for developing stacks composed of multiple honeycomb cells. A comparison with numerical calculation by the finite element method also gives information for further improvement of the cell..